Preparation of diaryl amines



June 8, 1937. M. F. ACKEN PREPARATION OF DIARYL MINES Filed-Jan. 28, 1936 Mam/5a fT/Icken, INVENTOR.

ATTORNEY.

Patented June 8, 1937 warren STATES PATENT orrice PREPARATION OF DIARYL AMIINES Marshall F. Acken, Woodbury, N. J., assignor to E. I. du Pont de Nemours & Company, Wilmmgton, DeL, a corporation of Delaware Application January 28, 1936, Serial No. 61,141

4 Claims.

have comprised heating the particular primary aromatic amine under suitable pressure and in the presence of a catalyst. For example, a wellknown method for, the preparation of diphenylamine has involved heating aniline together with small amounts of a hydrogen halide in an autoclave under a pressure of about 300 lbs. per sq. in. V

and at a temperature of about 300 C. The autoclave employed in processes of that nature is provided with a reflux condenser so that, as the reaction mixture boils, the vapors of the primary amine and diaryl amine formed, or in particular the vapors of aniline and diphenylamine, are condensed and returned to the autoclave. In the art, such reflux condensers consist essentially in a column of wrought iron pipe attached to the head of the autoclave and extending downward therein for a short distance. In the upper region of the column, connections are provided for temperature control and for releasing vapors such as ammonia and aniline as desired. Water cooling may be effected by run-' ning a, film of water down the outside surface of the condenser.

Although these columns are satisfactory from the standpoint of heat transfer, they have the serious disadvantage that they are rapidly corroded by the vapors present in the column. Since the rate of corrosion is not at all uniform over the whole surface of the column, holes may develop, permitting the escape of poisonous and inflammable aniline vapor under high pressure. This results in a serious safety hazard in addition to a reduction in efficiency due to a substantial curtailment in the length of life of the column.

An object of my invention is to provide an improved process for refluxing vapors in the presence of corrosive matter in a pressure system.

Another object of my invention is to provide an improved process for the preparation of diaryl amines. A further object is to provide an improved process for the preparation of diphenylamine. Additional objects will appear from the more detailed description of my invention which follows.

These objects are accomplished by the following invention in which I have found that a higher 5 degree of safety and a greater efficiency through the longer life of columns result from the use of a corrosion-resistant material as the refluxing surface or liner, supported by a pressure-resistant material as a jacket for such a liner in reactions involving refluxing in the presence of 5 corrosive vapors under pressure, said arrangement being rendered practical by the interposition of 'a suitable heat transfer agent between the jacket and liner, said medium being selected from the standpoint of safety. 1

For instance, I have found cast iron to be a suitable material for construction of the refluxing surface, but this material possesses the disadvantage of mechanical weakness. Therefore,

a supporting jacket of pressure-resisting mate- 1 rial was placed around the corrosion-resistant liner so that an annular air space was formed between the two. Although the construction could be carried out so that this intervening space was rendered very small, yet its presence was 20 still undesirable from a standpoint of heat transfer, since the flow of heat from liner to jacket was so reduced that insufficient refluxing occurred.

I have discovered that this difiiculty may be overcome, without undesirable complications, by the introduction of a suitable heat exchanging medium. into the annular space between the liner and the jacket, said medium being held in place by a tight joint at the bottom of the column. In 30 choosing the material for use as the heat transfer. agent, it is desirable from the standpoint of safety to select one relatively inert with respect to the materials present in the reaction chamber. This eliminates the danger of loss of life or ap- 35 paratus, or loss of efficiency of the process, all of which can be caused by the occurrence of foreign reactions; that is, any reactions other than those intended, such foreign reactions often being effected by leaks in apparatus or faulty con- 40 struction. If the heat transfer medium is sufficiently inert with respect to the reactants, it is even unnecessary to shut off the top of the annular space from the top of the central reflux column. This is particularly true when the me- 45 dium comprises one of the products of the principal reaction.

For example, in the preparation of diphenylamine from aniline, heated under pressure with a catalyst, the space between the liner and the 50 jacket may be filled with molten diphenylamine. This preferred embodiment of my invention is illustrated by the drawing, in which the reflux column comprises the cast iron liner I, supported by the steel jacket 2, creating the column space 3 and the annular space 4. The annular space is shown open at the top 5, and partly filled with diphenylamine 5. This material has a heat transfer coefficient approximately seven times that of air or aniline vapor. The resulting reflux process is satisfactory either in winter or summer operations, and at the same time greater safety and eificiency are accomplished.

However, this particular embodiment is not to limit the scope of my invention. I have discovered in general that a safer and more effieient reflux may be carried out in pressure systems by the use of corrosion-resistant means supported by a pressure-resistant means, these means being maintained in heat exchanging relation by the interposition of any suitable heat transfer agent selected from the standpoint of its stability in relation to the rest of the system. The annular space containing the heat transfer medium may be either open or closed at the top, at will, depending upon the nature of the heat transfer agent employed.

The application of my invention is not to be limited to the process for the preparation of diphenylamine, but is useful in any system in which a heat transfer is necessary, or in which the safety of the process may be enhanced by the choice of a suitable heat transfer agent. The invention is especially applicable in similar processes for the manufacture of other diaryl amines from their various respective primary aromatic amines such as the anilines, toluidines, Xylidines, naphthylarnines, and phenetidine, for example the ditolylamines, dixylylamines and aryl-alphanaphthylamines such as N-phenyl-alpha-naphthylamine and N-p-tolyl-alpha-naphthylamine, the preferred heat transfer agent in each case comprising the particular diaryl amine under preparation.

As many apparently widely different embodiments of this invention may be made without departing from the spirit thereof, it is to be understood that I do not limit myself to the foregoing embodiments or description except as indi cated in the following patent claims:

I claim:

1. In the process of heating together chemical reagents under pressure wherein said reagents are refluxed in the presence of corrosive vapors by passing in contact with a corrosion-resistant material supported by a cooled pressure-resistant material, the step of interposing between said materials a heat-exchanging medium comprising essentially a material substantially inert with respect to the principal reactants.

2. The process of claim 1, in which the heatexchanging medium comprises essentially a product of the principal reaction.

3. In the process of preparing diaryl amines under pressure wherein corrosive vapors are refluxed by passing in contact with a corrosionresistant material supported by a cooled, pressure-resistant material, the step of interposing between said materials a heat-exchanging medium comprising essentially the diaryl amine under preparation.

4. In the process of preparing diphenyl amine from aniline under pressure wherein such reagents are refluxed in the presence of corrosive vapors in a pressure-resistant column provided with a corrosion-resistant inner tube, the step of interposing between said column and said inner tube a heat-exchanging medium comprising essentially diphenyl amine.

MARSHALL F. ACKEN. 

